Short Communications: Crystal structure of a C2-symmetric Schiff base from 1,4-diacetyl-2,3,5,6-tetramethoxy benzene and (S)-1 -phenylethylamine

The title compound was prepared by a TiCl4-catalyzed reaction of bisacetylated benzene and 1-phenylethylamine. It crystallizes from ethyl acetate/petroleum ether orthorhombically in the space group Ρ2{λχ2 with a = 796.2(1), b = 1908.7(5) and c = 924.1(2) pm. Introduction Schiff bases derived from nucleus-substituted benzenes and 1-phenylethylamine have proved to be useful intermediates in the stereoselective synthesis of optically active substituted 1-arylethylamines (Bringmann, Geisler, Geuder, Künkel and Kinzinger, 1990; Bringmann, Geisler and Jansen, 1989). For one of these imines, the compound 1, we have recently been able to perform an X-ray structure analysis, which, to our great surprise, showed an unexpected Z-configuration at the C,TV-double bond, apparently despite the steric hindrance (Peters, von Schnering, Bringmann, Geuder, 1992). In order to see whether this unexpected configuration is unique in this case or reflects a more general principle, we have prepared the corresponding 122 Κ. Peters, Ε.-Μ. Peters, Η. G. von Schnering, G. Bringmann and T. Geuder Table 1. Local parameters ( χ 10) and equivalent isotropic displacement parameters (pm χ 10"').